1. Field of the Invention
The present invention relates to a wireless local access network (WLAN), and more particularly, to an interworking procedure with an external network in a WLAN, a station supporting the interworking procedure, and a message format for the interworking procedure.
2. Description of the Related Art
With the development of information communication technology, a variety of wireless communication technology has been developed. A WLAN permits wireless access to intra network and/or Internet in specific service areas such as home or companies or air planes by the use of portable terminals such as a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP) on the basis of radio telecommunication technology.
These days, thanks to the increased availability of WLANs, portable terminal users such as laptop computer users are able to perform their tasks with increased mobility. For example, a user can take his laptop computer from his desk into a conference room to attend a meeting, still have access to his local network to retrieve data, and have access to the Internet via one or more modems or gateways present on the local network without being tethered by a wired connection. Similarly, business travelers commonly use their portable terminals to gain access to their email accounts, to check if there is any unread email, and to read and send email.
In the initial WLAN technology, a data rate of 1 to 2 Mbps was supported by the use of frequency hopping, spread spectrum, and infrared communication using a frequency of 2.4 GHz in accordance with the IEEE 802.11. In recent years, with the development of the wireless communication technology, 54 Mbps in maximum can be supported by applying the orthogonal frequency division multiplex (OFDM) technology, etc. to the WLAN. In addition, the IEEE 802.11 has developed or is developing wireless communication technologies for improvement in quality of service (QoS), compatibility of an access point (AP) protocol, security enhancement, radio measurement or radio resource measurement, wireless access in vehicular environment, fast roaming, mesh network, inter-working with external networks, wireless network management, and the like.
On the other hands, the IEEE 802.11u standard which is a kind of WLAN standards describes an interworking service in the WLANs. The main purpose of the interworking service is to permit the transmission of information from an external network for WLAN users, to help selection of connection networks, and to enable an emergency service. The IEEE 802.11u standard prescribes medium access control (MAC) and physical layer (PHY) protocols necessary for accomplishing the main purpose.